Genome-wide analysis of leucine-rich repeat-only proteins gene family revealed FaLRRop26 responding Colletotrichum Siamense infection by regulated lignin synthesis in cultivated strawberry (Fragaria × ananassa)

BACKGROUND: Strawberry (Fragaria × ananassa Duch.) is a highly valued crop, susceptible to various diseases, with Colletotrichum siamense-induced crown rot being a major concern. Emerging evidence indicates that leucine-rich repeat only protein (LRRop) participates in plant responses to both biotic and abiotic stresses. RESULTS: The LRRop gene family was investigated in strawberry. 140 FaLRRop gene family members were identified in the strawberry genome, and 121 orthologous gene pairs with F. vesca and 117 with F. iinumae. C. siamense infection and exogenous MeJA pretreatment inhibited the expression of FaLRRop26 and its alleles, while SA pretreatment upregulated their expressions. The FaLRRop26 and its alleles mutations of octoploid strawberry were achieved by utilizing CRISPR/Cas9 gene editing. Mutants exhibited significantly larger lesions compared to wild-type. Compared with wild-type, the key structural genes for lignin monomer synthesis, including 4-coumarate: CoA ligase, caffeic acid-O-methyltransferase, ferulate-5-hydroxylase, cinnamoyl-CoA reductase and cinnamyl-alcohol dehydrogenase of mutants were significantly inhibited. Furthermore, mutants had 17% lower lignin content than wild-type on 0 days post-inoculation (0 dpi). On 4 dpi, wild-type accumulated approximately 87% lignin, whereas mutants maintained only about 30%. CONCLUSIONS: Our findings suggest that FaLRRop26 and its alleles enhanced strawberry resistance for C. siamense by positive regulating lignin biosynthesis, and which provides new insights into the role of LRRop gene family in strawberry immunity and offers a potential target for strawberry resistance breeding.